The present invention relates to a process for the manufacture of vinylidene fluoride from 1-chloro-1,1-difluoroethane. Vinylidene fluoride is a valuable monomer for the preparation of homopolymers and copolymers which exhibit high chemical resistance and heat resistance.
Vinylidene fluoride is usually prepared by thermal dehydrochlorination of 1-chloro-1,1-difluoroethane. It is known to use promoters for this reaction. For example, the pyrolysis of 1-chloro-1,1-difluoroethane can be initiated by amounts of carbon tetrachloride which are between 0.5 and 200% by weight, and preferably, between 2 and 25% by weight, of the 1-chloro-1,1-difluoroethane, as disclosed in U.S. Pat. No. 2,628,989, granted Feb. 17, 1953, in the name of Allied Chemical and Dye Corp. In U.S. Pat. No. 2,628,989, the presence of extraneously introduced elemental chlorine, even in very small amounts, is said to be detrimental to the reaction and causes the formation of undesirable by-products.
It has also been proposed to use chlorine by itself as a promoter, in an amount of 0.5 to 4% by weight of the 1-chloro-1,1-difluoroethane, as disclosed in French Pat. No. 1,458,285, filed on July 28, 1965, in the name of Pennsalt Chemicals Corp.